In a membrane pump, it is known to separate the working chamber from the hydraulic control chamber by means of a double flexible wall constituted by two parallel membranes. This disposition increases operating security since a break in one of the membranes does not cause the pumped fluid to propagate into the moving parts of the pump. Such propagation is to be avoided since the fluid driven by the pump is often corrosive in nature.
In order to provide means for monitoring the state of the membranes, the space between them is put into communication with the outside of the pump by means of a duct provided with a discharge valve. Thus, a flow through said duct constitutes a sign that a membrane has broken.
A practical implementation of such break detection comprises an annular spacer interposed between the peripheral portions of the two membranes. A radial passage is provided through said spacer leading to the space between the membranes. In order to ensure that the end of said passage is not closed by the membranes (with the volume between the membranes being kept to a minimum during operation of the pump) a groove is formed in the inside surface of the spacer to constitute the peripheral extremity of said space, and the opening of said duct opens out into the bottom of the groove.
It is also common practice for the two membranes and the intermediate spacer which is sandwiched between the membranes to be fixed in the body of the pump by clamping between an annular bearing surface provided on the pump body (on its hydraulic control chamber side) and an annular bearing surface provided on the pump head (on its working chamber side) when said head and body are assembled to each other. More precisely, these bearing surfaces are provided in the front and rear grids for supporting the membranes in each of their extreme positions.
One of the consequences of this mode of assembly and of the vacuum set up between the membranes by the external pressure is that as each of the membranes moves back and forth, it tends to extrude itself into the groove in the annular spacer. This tendency is an important factor in membrane damage, and it rapidly gives rise to breakage.
The invention seeks to remedy this fact by providing an improved device for detecting that a membrane has broken, which device is also easier to manufacture and cheaper than prior devices.